1. Field of the Invention
This invention relates to fluid-film bearings for rotating machinery and more particularly to journal bearings which include resilient bearing-inserts for efficient support of high-speed rotors.
2. Description of the Prior Art
Rigid and rigidly-mounted fluid bearings have limitations imposed by speed and mass, which govern the onset of instability. The latter, referred to generally as "half-frequency" and "fractional frequency" whirl, causes a sudden growth of amplitudes of the journals, at a speed when self-excited vibrations set in, and generally leads to bearing and machine damage, or destruction. Furthermore, such bearings are not tolerant of misalignment, temperature gradients and elevated temperatures, dirt and foreign particles and, further, do not respond favorably to shock and impact, especially in the case of gas bearings. In the case of the latter, operation is very sensitive to changes in clearance, so that in the presence of thermal gradients an adverse effect of performance is almost unavoidable. Bearings of expensive and complex construction, such as pivoted-shoe bearings, circumvent some of the foregoing problems, but introduce others such as pivot fretting, shoe flutter and difficulties of assembly. In addition, they are expensive and stability is not insured. Recent efforts to improve journal bearings have resulted in a variety of foil bearings, some of which are shown in U.S. Pat. Nos. 3,635,534; 3,747,997; 3,795,427 and 3,809,443 and in the publication by L. Licht and M. Branger entitled "Motion of a Small High-Speed Rotor in 3 Types of Foil Bearings", Journal of Lubrication Technology, Trans. ASME Vol. 97, Ser. F, No. 2, April 1975, pp. 1-11. While various prior art foil bearings are known to provide remedies to some of the foregoing difficulties, flexibility without adequate damping will not insure stability, and the introduction of compliance cannot be accomplished at the expense of other important bearing characteristics. Also, certain of the prior art bearings suffer the disadvantage of having foil supports characterized by sharp creases prone to crack propagation or by corrugations prone to buckling.
In sum, although the prior art techniques may be useful, the need for further improvements has remained. Unquestionably, there is a need for an improved fluid-film journal bearing for the support of high-speed rotors (such as turbocompressors, turbochargers, turbogenerators, turbine gas generators, cryogenic expanders, blowers, pumps, aircraft air-cycle machines, centrifuges, scanners, yarn spinners and processors and the like).